Invariance is a fundamental phenomenon in mathematics. In this combinatorics problem from ISI Entrance, we discuss how to use invariance.

<script src="https://apis.google.com/js/platform.js"></script>

<div class="g-ytsubscribe" data-channelid="UCK2CP6HbbQ2V6gn8Xp_vM-Q" data-layout="full" data-count="default"></div>